Caisson



A. G. llizo'rnuoFF CAISSON Aug. 6, 1935.

Filed Sept. .30, 1935 2 Sheets-Sheet 1 Aug. 6, 1935. l A. G. RoTlNol-F 2,010,199

CAISSON Filed Sept. 30, 1933 2 Sheets-Sheet 2 Exil Patented Aug. 6, 1935 UNITED `STATES PATENT OFFICE Application september 30, 1933, serialNo. 691,703 In Great Britain October 1, 1932 7 claims. (o1. s1- 81) the sides of the caisson and the surroundingy earth or soil. Naturally a large factor of safety is allowed in determining the safe load per square foot as the soil at the bottom and sides is in no way consolidated, but rather weakened by the sinking operation. An allowance also has to be made for the human element of placing the concrete for the seal at the base of the caisson and the fact that sometimes the seal has to be placed in position through water. No method now exists for readily checking the bearing capacity of the caisson except by test loading, which is an Vexpensive and lengthy process. g y' In accordance with my invention, a suitable kentledge or load upon the caisson is utilized to deliver hammerlike blows directly to the caisson in order toforce it down, overcomeits skin friction and consolidate and compress the ground under and around the base of the caisson either before or after the seal is placed in' position in the caisson. This increases the bearing value of the ground carrying the caisson, and therefore ensures a much greater l-oad carrying capacity of the caisson. It also makes it possible to determine scientifically, practically and readily, the safe load carrying capacity of each caisson.

It will be appreciated that from a consideration of the energy of the falling kentledge and 40 the capacity of the caisson to withstand the applicati-on of the energy without further penetra tion into the soil, the loadcarrying capacity of the caisson can be determined. The caisson after reaching suitable strata, may if desired be "sealed internally either before or after the application of blows by the kentledge. The hammering may be effected by raising the kentledge by piston or pistons operated upon by compressed air; steam or gas or internal combustion, and then allowing the kentledge to fall upon suitable surfaces of the caisson.

The kentledge which consists of a plurality of units secured together may be of any suitable form, and be constructed to deliver theblows to 5K5 the caisson. Preferably it is of annular form and disposed so that the excavating and discharge operations are eiected through the central area bounded by the kentledge.

In cases where a caisson is sunk by excavating at the bottom thereof by compressed air jets 5 and by discharging the material through a discharge pipe leading up out of the caisson, the kentledge can be disposed around the discharge pipe and the latter may be used to guide the kentledge.

The compressed air may be suppliedto the base of the caisson from a recess around the inside of the caisson shaft or inside the bottom` of the discharge pipe, so that after soil has been forced up inside the caisson or up the discharge l pipe by the energy of the falling kentledge o1' initially by the weight of the caisson, the admission of compressed air to the annular recess will cut off the soil which has penetrated above the recess, and force it up the discharge pipe. 20

The bottom of the caisson may have a cutting edge and air jet apertures may also be disposed adjacent to such edge.

Referring to the accompanying explanatory drawings:- 25

Figure 1 is a sectional elevation of a caisson constructed and arranged in one convenient form in accordance with the invention. The section of the upper part of the caisson'is taken approximately on the line I-I of Figure 3. 30

Figure 2 is an elevation showing the upper part of the caisson shown in Figure 1, the view being taken at right angles to Figure l.

Figure 3 is a sectional plan view on the line 3 3 of Figure 2. 35

Figure 4 is a sectional plan view on the line 4-4 of Figure 1.

Figure 5 shows a modified construction and arrangementof caisson.

Figuresl' and 'l are respectively sectional elevation and plan of the weights constituting the kentledge employed for driving the caisson into the soil. y Y

The same reference letters in the different views indicate the same or similar parts.Y 45

The caisson consists of an outer casing a which may be made of steel or of concrete and which is adapted to line the hole formed by the cutting edge provided at the lower end of the casing. Within such casing is a double walled mandrel c 50 which at its lower end is provided with a `base ring d and flanged to rest upon the lower part e of the casing w which is shaped to provide a cutting edge. The upper end of the mandrel has `a head piece f resting thereon which forms an air inlet manifold for a series of cylinders y which rise and fall over stationary hollow pistons h within them. Alternating with said pistons and reciprocating cylinders are dollies i, which normally support annular weights i constituting kentledge for the caisson as hereinafter described. The dollies z' are carried by brackets 7c upon the base ring f. As a continuation of the mandrel c is a discharge tube c1 for the delivery of the material which is squeezed or forced into the interior of the mandrel during the driving of the latter and the casing d into the soil. The space m between the double walled mandrel c serves for the passage of compressed air from the inlet pipe n to the jet orices o at the base of the mandrel, said orifices being located in a r cess as shown so as to be clear of the material forced up the mandrel.

Distance pieces p upon the exterior of the mandrel serve to maintain the mandrel and casing co-axial.

In operation, the caisson may be placed in position where it is to be sunk, and the soil or the like will be pressed up the mandrel c so that it passes the row of jet orices o. Compressed air is then turned on to the orices and it cuts through the material by its expansive force and forces the part above the jet orirlces up the mandrel and through the discharge pipe c1. This is indicated in Figure l where the separated plug of earth about to be discharged is shown at q. As the downward movement of the caisson becomes slower, compressed air is passed intermittently to the cylinders g which rise and lift the kentledge 1i, and then fall as the air is released therefrom and allow the kentledge to fall by gravity and impart a blow to the mandrel c which drives the casing a with its cutting edge deeper into the earth, so forcing a further plug of earth up the mandrel for discharge by compressed air through the jet orices o as before.

Gradually the rate of descent of the caisson will lessen until a set is reached when by a consideration of the energy represented by the falling kentledge, the load carrying capacity of the caisson can be calculated. The mandrel c can now be withdrawn and the caisson concreted and sealed.

It will be seen that by the use of the blows imparted by the kentledge, the ground under and around the base of the caisson is compressed and consolidated, and not weakened as with present methods of sinking caissons. The rate of descent r sinking of the caisson under the said blows provides data as to the load carrying capacity of the ground and the skin friction of the caisson, as sinking proceeds, so that sinking can be stopped when a suitable set is reached, with corresponding economy. In addition, it may be possible with my improvement to sink caissons of smaller cross section than usual to carry safely a predetermined load because accurate data is given of the load carrying capacity of the caisson throughout the sinking operation until the desired set is reached.

As shown in Figure 5, the mandrel tube c2 is made to form a pilot cutter at its lower end which is driven into the earth in advance of the caisson casing as is illustrated, and is then withdrawn upwards so that the cutting edge of the casing breaks away and compresses inwards the wall of soil left around the central space vacated by the pilot mandrel. The contents of the pilot tube are discharged by compressed air from the air jet orices o1 as in Figure 2. The pilot tube and the casing may iinally be secured together for simultaneous driving or the casing alone may be driven to the iinal set.

rIhe weights constituting the kentledge are shown in Figures 6 and 7. Each weight is a half `ring and the abutting faces are secured together by bolts t. The superposed rings are secured together by clamps u, held in place by headed bolts 'u with cotter pins w therethrough. The weights in the adjacent rows break joint with one another for obvious reasons.

`Generally when sinking a caisson the soil around and at the bottom of the caisson is disturbed and considerably weakened by the excavating and sinking operations. In accordance with my invention, when during the sinking of a caisson, it is revealed that a suitable bearing strata is reached, 'this strata is mechanically compressed and consolidated over and above its natural state, and in order to increase its load carrying value, this consolidation or compacting can take place either before or after the base of the caisson is sealed.

It will be understood that whilst my invention has been illustrated as applied to a caisson in which the excavation is effected by compressed air assisted by the action of the blows of the falling kentledge which cause the material to be excavated to use in the interior of the caisson, it may be applied to caissons in which the excavation is eiected manually or by mechanical grabs or other appliances. In addition, the blows of the kentledge may be applied to the caisson itself where this is made of reinforced concrete and the compressed air where such is employed may be passed through passages and ports in the caisson itself.

In existing sinking methods, a dead weight is used to overcome the skin friction of the caisson. The caisson is built as heavy as possible; in many instances a static kentledge or load amounting sometimes to several thousands of tons is added to increase the weight of the caissons. In my method the caisson can be made very light, and the dynamic force of a falling kentledge of much smaller weight is sufficient to sink the caisson and to obtain the set. The use of kentledge to deliver blows to the caisson facilitates the forcing of the material in the form of a plug up the inside of the caisson which can be readily cut off and discharged. Great economy of air required for excavation is thereby effected. When the plug has been sheared across by pressure of the air, the expansion of a small amount of air is suflicient to force the plug up and out of the caisson. In the latter case not the kinetic energy of airis used for excavating and discharging, but the pressure and expansive force of the air.

What I claim is:

1. A method of sinking a caisson and obtaining the required load-carrying capacity comprising mounting a kentledge around the discharge branch of the caisson, raising said kentledge and withdrawing support from said kentledge in its raised position whereby said kentledge is caused to fall and to impart a downward blow to said caisson to wedge material up the inside of the latter.

2. A method of sinking a caisson and obtaining the required load-carrying capacity comprising mounting a kentledge upon the caisson, raising said kentledge and withdrawing support from said kentledge in its raised position whereby said kentledge is caused to fall and to impart a downward blow to said caisson, thereby causing said caisson to sink and to force soil up the interior of said caisson, and subsequently forcing air into the soil within the caisson at the lower extremity thereof to such an extent as is necessary to raise said soil up the caisson in the form of a plug and to expel same from the caisson by the expansive force of the compressed air.

3. A method of sinking a caisson and obtaining the required load-carrying capacity comprising mounting a kentledge upon a mandrel located within and supported by a caisson casing, raising said kentledge and withdrawing support from said kentledge in its raised position whereby said kentledge is caused to fall and to impart a do-wnward blow to said mandrel and therethrough to said caisson casing, thereby causing said mandrel and said caisson casing t sink and to force soil up the interior of said mandrel, and subsequently forcing air into the soil within the mandrel at the lower extremity thereof to such an extent as is necessary to raise said soil up the mandrel in the form of a plug and to expel same from the mandrel by the expansive force of the compressed air.

4. A method of sinking a caisson which comprises raising a kentledge carried by said caisson and withdrawing support from said kentledge while in the raised position whereby said kentledge is caused to fall and to impart a downward blow to said caisson to force soil up the interior of said caisson, and excavating said soil by means located wholly within said caisson.

5. A method of sinking a caisson which comprises inserting a hollow mandrel within the caisson movable vertically with respect thereto, mounting a kentledge upon said mandrel, raising said kentledge, withdrawing support from said kentledge when in its raised position thereby causing said mandrel to sink and to force soil up the interior thereof, excavating said soil by means located wholly within said mandrel, and raising said mandrel to withdraw it within the caisson.

6. A caisson comprising a casing, a mandrel co-axial within said casing and capable of driving the latter, a kentledge supported upon said mandrel, means adapted to raise said kentledge and to be withdrawn from support of saidkentledge to cause it to fall by gravity to impart a blow to said mandrel and to the casing, and air admission orices within said mandrel at the lower end thereof adapted to cut off and expel upwards through the mandrel in the form of a plug any material forced into the mandrel by the sinking of the caisson.

7. In a caisson as claimed in claim 6, the kentledge being in the form of rings of weights, each Weight constituting half a ring, the half rings and superposed rings being clamped together to form a unit around the discharge pipe of the caisson.

ALEXANDER GEORGE ROTINOFF. 

